The present invention relates to a slackening type blasting method for excluding by excavating part of a sloping surface formed by a base rock layer at one side, or both sides, of a road upon establishing or expanding of the road, or for excavating a part of a middle portion of a base rock layer
In general, there is a need to cut out a sloped surface made of base rock layer in road construction work for establishing or expanding a remote hill road, or a seashore road along mountain topography. In this case, excavating work of a base rock slope is executed by utilizing heavy-duty equipment such as a large type braker or excavator. In order to prevent accident or damage of passing vehicles during operation, a problem occurs in which mechanical excavating work utilizing the heavy duty equipment is decreased in its excavating efficiency, and a working term becomes longer when the sloped base rock layer is a hard base rock layer which is high in base rock strength. In such a case, cutting out the sloped rock surface is executed by a blasting method utilizing explosives.
In accordance with the blasting method of prior art, a so called mobile type blasting method has been used in which explosives filled in a number of blasting holes pierced into a base rock layer are detonated so that the base rock layer is completely released from the mother rock via its blasting pressure.
However, since the mobile type blasting method of the prior art increases the blasting pressure by using large quantities of explosives in order to completely release the base rock layer of a part desired to be cut out from the mother rock, there has been a problem of blasting noise, and that a part of base rock broken upon blasting flies far away from the blasting site to a remote place. But also a blasting vibration coming from the blasting pressure is transmitted far away. Consequently, the blasting has been done by laying a mat made of rubber material or a straw bag etc. on the base rock surface so that the blasting noise is decreased and the broken base rock layer particles cannot be flied. But, since the rubber mat and the straw bag covered on the base rock layer fly away together with broken base rock particles by the blasting pressure, it is hard to expect an effect capable of largely decreasing the blasting noise and vibration. And in a case when human dwelling houses and the like are located within 100 m near a construction working site, there is a problem that an application of a blasting method is difficult to safely implement and a passing of neighboring roads should be isolated.
A base rock layer made of hard rock has to be cut out with a predetermined width at a construction site for establishing or expanding the mountain road or seashore road. Dwelling houses and livestock facilities scattered within 100 m from that construction working site and public establishments due to the exploding noise and the blasting vibration and the like produced upon blasting the base rock layer, not only the dwelling residences are exposed to noise but also flying stones are thrown into residences. Also, the building is shaken due to the blasting vibration or a ground-sinking phenomenon occurs. Furthermore, a problem is arisen which gives vast casualties to various animals bred in livestock facilities. Still further there is a worry about producing casualties which induces an accident due to influence of exploding sound.
Accordingly, it is a primary object of the present invention to provide an improved blasting method which provides improved and sound abatement to surrounding areas.
It is another object of the present invention to provide a method using an improved blasting mat for achieving the improved safety and sound abatement features of the improved blasting method.
These and other objects are fulfilled by providing a slackening type blasting method for separating rock layers in a blasting region from surrounding mother rock by generating a crack formation, comprising the steps of, dividing the blasting region into a plurality of sub-regions in a top surface of the base rock; drilling each sub-region with a plurality of vertically oriented blasting holes with predetermined spacings therebetween; inserting explosives into each blasting hole; connecting the explosive with a lead wire electrically connected to a detonator; covering the blasting region with a blasting mat including, a metal plate having a bottom surface for covering a blasting region, said plate having a thickness capable of containing blasting forces within said region; an elastic barrier connected to the periphery of the bottom surface for dampening blast noise and containing flying debris generated by the blast; and a frame having a substantial weight resting on a top surface of the metal plate, said frame having metal beams in a grid configuration overlying the top surface of the metal plate; and operating the detonator to successively detonate explosives in the blasting holes in accordance with a predetermined order to thereby generate said crack formation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.